I'm guessing it would get you about 12 hours if you got it straight off the charger and played till it died, but I'm not 100% sure. You should be fine as long as you plug it in once your finished playing it. I just usually forget to do it and that's, more than likely, why it goes off on me.
If you get one, just remember to plug it in to charge before you bring it on any long trips and it should be fine.